Individuals may suffer from a variety of ankle foot gait pathologies, such as muscle weakness in the anterior and/or posterior compartments of the leg, which severely inhibit locomotory function. For example, drop foot gait is the inability of an individual to lift or dorsiflex their foot because of reduced or no muscular activity, typically in the anterior compartment of the leg around their ankle. The major causes of drop foot include stroke, cerebral palsy, multiple sclerosis, and neurological trauma from accident or surgical complication. The two major complications of drop foot are slapping of the foot after heel strike (foot slap) and dragging of the toe during swing (toe drag). At heel strike, the foot generally falls uncontrolled to the ground, producing a distinctive slapping noise (foot slap). During mid-swing, toe drag prevents proper limb advancement and increases the risk of tripping.
A conventional approach to the treatment of drop foot gait is a mechanical brace called an Ankle Foot Orthosis (AFO), which has increased in popularity over the last several years. Although AFO's offer some biomechanical benefits, disadvantages still remain. For example, APO's do not improve gait velocity or stride length, in children with cerebral palsy. Further, although a constant stiffness AFO is able to provide safe toe clearance in drop foot patients, the device does not reduce the occurrence of slap foot at all walking speeds.